In the related art, an integrated circuit (IC) obtained by connecting a plurality of transistors or resistors so as to form an electrical circuit and integrating them into one chip has been generally used in a main portion of a computer or a communication apparatus. In addition, there is a power semiconductor element as a semiconductor element which is used to switch a higher voltage or a larger amount of current than the IC. Examples of the power semiconductor element include an insulated gate bipolar transistor (hereinafter, referred to as an IGBT) and a diode.
Here, an IGBT producing process according to the related art will be described. First, a surface element structure portion including a base region, an emitter region, a gate oxide film, a gate electrode, an interlayer insulating film, an emitter electrode, and an insulator passivation is formed on the front surface side of a wafer. The emitter electrode is, for example, an aluminum-silicon film. The insulator passivation is, for example, a polyimide film. Then, a polyimide passivation is formed on the front surface of the wafer.
Then, a surface protective tape is attached to the front surface of the wafer on which the polyimide passivation is formed and the rear surface of the wafer is ground such that the wafer has a desired thickness. Then, for example, a collector layer is formed on the rear surface of the wafer. Then, a plurality of metal materials, such as aluminum, titanium, nickel, and gold, are formed on the rear surface of the wafer, that is, the surface of the collector layer by vapor deposition to form a collector electrode. Finally, a dicing tape is attached to the collector electrode and the wafer is diced into a plurality of chips. In this way, the IGBT is completed.
In general, the surface protective tape which has been used in the related art is a combination of a base layer and an adhesive layer (including an intermediate layer) and has a thickness of, for example, 150 μm. In addition, as the surface protective tape, a hot-melt sheet has been known which includes at least a hot-melt layer with a melting point of 105° C. or less and is heated and stuck to the surface of a semiconductor wafer (for example, see the following Patent Document 1).
As a method of attaching the surface protective tape to the front surface of the wafer as described above, a method has been proposed which attaches a surface protective tape including a base layer and an adhesive layer to the surface of a semiconductor wafer which has unevenness caused by a polyimide passivation and heats the surface protective tape to deform the base layer and the adhesive layer, thereby substantially flattening the surface of the base layer (for example, see the following Patent Document 2).
As another method, the following method has been proposed. A protective tape is supplied onto the surface of a semiconductor wafer and is rolled and moved while being pressed by a sticking roller. The protective tape is attached to the surface of the semiconductor wafer. The attached protective tape is cut along the outer circumference of the semiconductor wafer. Then, a pressing member presses the upper surface of the protective tape to flatten the surface of the protective tape (for example, see the following Patent Document 3).
As another method, a method has been proposed which sticks a semiconductor wafer protective adhesive sheet obtained by sequentially laminating a base, at least one intermediate layer, and an adhesive layer to the surface of a semiconductor wafer. In the method, the adhesion temperature between the adhesive sheet and the semiconductor wafer is in the range of 50° C. to 100° C. and the loss tangent (tan δ) of the intermediate layer which comes into contact with the adhesive layer at the adhesion temperature is equal to or greater than 0.5 (for example, see the following Patent Document 4).
As another method, a method has been proposed which includes a heating step of heating a mounting means on which a workpiece is placed using a heating means, a drawing step of evacuating a pressure chamber, which accommodates the mounting means and the workpiece placed on the mounting means and can be hermetically sealed, using a drawing means, a sticking step of moving the workpiece close to a tape member and sticking the workpiece to the tape member after the chamber reaches a vacuum, and a pressurization step of operating a pressurization means to introduce air into the pressure chamber in a pressurized state after the sticking is performed for a predetermined period of time in the adhesion step (for example, see the following Patent Document 5).